The prior art in the field of playground equipment discloses a variety of structures, particularly for outdoor use, designed to provide a three-dimensional spacial network where children can climb. Examples of such amusement appliances are found in the following Japanese Utility Model publications:
Publication Serial Number date Filing Date Applicant SHO-58-37477 Sept. 17, 1980 March 7, 1979 Toshiko Horiuchi SHO-59-25410 Sept. 8, 1980 March, 6, 1979 Toshiko Horiuchi SHO-50-20826 Feb. 6, 1973 June 17, 1971 Mitsuru Senda
More specifically, the amusement appliances include a series of net units suspended from vertical posts. The attachment points of the individual nets to the respective posts are at different vertical elevations so the nets acquire a non-planar configuration. In a particular embodiment, the individual net units are disposed around a main central post and they are suspended from it at a predetermined distance from the ground, say generally at least two meters. The individual net units slope downwardly, toward smaller posts at the periphery of the spacial-network to hold the free edges of the nets and thus maintain a level of tension and stability in the whole structure.
Advantageously, the net units are made from a material that has a certain resiliency. This feature enables the net units to stretch repeatedly and contract when children climb or jump on them, thus enhancing the overall enjoyment provided by the apparatus. However, this otherwise desirable characteristic leads to an increased strain on the various posts that support the net units above the ground. For instance, when a group of children is climbing and jumping on only one side of the spacial network of net units, rather than being spread over the entire playing surface of the network, significant bending moments are induced particularly in the central post.
One approach of providing a robust supporting structure that is capable to resist the dynamic forces developed when the playing surface of the spacial network is heavily loaded, consists of casting in the ground heavy concrete blocks on which the various posts are anchored. However, this procedure significantly increases the cost of the playground appliance. Further the procedure is suitable only for permanent installations.